Since the app version 2.0.12 you can add a custom design based on projects to your Jira to have a nicer UI appearance or increase your corporate identity. By defining Project Themes the UI of your Jira will change, depending on the project (or the project category) you are currently in. To create a Project Theme navigate to the app administration and choose Project Themes & Style.
Now you can choose to which projects or project categories you want to apply your theme. Here you have a few options:
Option 1: Choose a project category but no project: Your theme will be applied to all projects in selected category.
Option 2: Choose a list of projects but no project category: Your theme will be applied to the selected projects.
Option 3: Choose a project category AND a list of projects: Your theme will be applied to all projects in selected category AND to the selected projects.
If you select Edit, you can configure the project themes in the same way as the global themes: